This invention relates to the field of ultrasonic measurement of a load or strain in a fastener member. More particularly, this invention relates to an ultrasonic transducer which is intended to be fixed on a fastener, and the resulting fastener.
The theory and use of ultrasonic techniques for measuring the load or strain in a fastener, such as a bolt, and apparatus therefor are well known in the art. See, for example, the patents to McFaul et al 3,759,090, McFaul 3,810,385, and Jones 4,413,518, the entire disclosures of all of said patents being incorporated herein by reference. The technique of ultrasonic measurement of load in a fastener involves the mounting of a piezoelectric ultrasonic transducer on the fastener to propagate ultrasonic waves in the fastener. Prior patents teach that the transducer can be removeably mounted on the fastener or contained in the head of a fastening tool, and a coupling medium, such as a coupling oil is used between the transducer and the fastener. Proposals have also been made to permanently mount the ultrasonic transducer on the fastener. See, e.g., U.S. Pat. Nos. 4,294,122 and 4,295,377 to Couchman and U.S. Pat. Nos. 4,846,001 and 4,899,591 to Kibblewhite, the entire disclosures of all of said patents being incorporated herein by reference.